My take, as a middle aged born again cyclist:
If you have a comfortable income, budget $800-1200 for a decent bike to get started with. Anything less, you start making compromises, anything more is personal jewelry. But it's pretty neat jewelry... Visit whatever bike shops are near you, get them to fit you properly. That's critical - even a small adjustment makes the difference between a long ride and numb hands. Pay the extra and get the bike locally, it will be the best investment you will make. I'd suggest you stick with the name brands - Trek, Cannondale, Giant, maybe a Klein. There are good deals on LeMond bikes right now, due to some ill conceived comments by Greg LeMond regarding Lance. But his bikes are terrific, very smooth riding.
Other gear you want to get - a speedometer, and a heart rate monitor. I'd suggest the Polar 150, it's fairly inexpensive, and tells you what you want to know. If it drops to zero, don't worry - either the wireless connection is getting interference, or it's too late to do anything about it.
Saddles - ride whatever the bike has on it for a month. If your butt is still killing you, welcome to the saddle search. It took me four saddles before I found one that I could ride for more than two hours. If you start getting an uncomfortable feeling right around the prostate, look for a seat with a cutout in the middle.
Clothes - if the idea of riding in tight lycra shorts makes you uncomfortable, get the baggy MTB shorts. When you whip your gut into shape, go for the lycra. Who cares what the men think - the first time a gal tosses you an apprecitave glance, it'll tickle you pink. On top of that, the lycra shorts are really comfortable on long rides, though I do draw the line at the crotch cream.
Snobs - they're out there, most of them young and insecure, that's why they're snobs. If they have to pump themself by looking down at other people, they're probably a little short in the self esteem department. You'll run into two types of cyclists, those with an attitude, and those that think that anyone riding any type of bicycle is doing something good. Stick with the latter, they're a lot more fun.
One other thing - if you apply yourself, you're going to see something that very few people over the age of 40 ever see - physical improvement. I got back into road bikes three years ago, had been riding MTB's for three years before that. Now, at age 48, I can do things I couldn't do at age 46, like pull that nasty hill near my house without stopping, or hold an 18mph average over rolling hills for 20 miles.